1. Field of the Invention
This invention relates to a method and an apparatus for molding polyurethane soles for footwear.
More specifically, the invention relates to the molding of soles for footwear using polyurethane of two different colors and/or physical and chemical properties. In the production of soles for sports shoes or the like, it is common practice to use a single material such as polyurethane or polyvinyl chloride; and to make the soles in two separate and distinct molding operations using different compositions for the two sole portions. The resulting soles have two differently colored portions and/or two portions with different properties such as hardness.
2. Discussion of Prior Art
One conventional two color molding technique is disclosed, for example, in applicant's Canadian Pat. No. 977,917, issued Nov. 18, 1975. In the conventonal method, a first mold cavity is formed at a first molding station where a first injection of moldable material is effected, and the mold is moved to a second molding station where a second mold cavity is formed and a second moldable material is injected into the second mold cavity. The first mold cavity is formed by a mold top in the form of a dummy last, mold sides or side rings and a mold piston. The second mold cavity is defined by the mold piston and first sole portion thereon, a lasted upper and different portions of the mold sides or another set of mold sides. In such a method, it is necessary to inject the moldable material at two separate locations to permit the first sole portion to at least partially cure to a hardness sufficient to prevent deformation thereof during the second injection. With the large injection units used to inject polyvinyl chloride, only one injection unit can be present at any one molding station.
It will be appreciated that the conventional method requires a large turntable with a plurality of molds--usually 20-24--in order to operate efficiently and economically. With a material such as polyurethane which requires an approximate 3 minute curing time, a large apparatus has been a necessity. Moreover, for two color injection a four component dispensing system is required, i.e. resin and hardener containers must be provided at each of the two molding stations. When injecting at two separate, spaced apart locations, the edge of the mold containing the injection port for the second material becomes clogged during the first injection step, thus making injection of the second material difficult if not impossible.
Thus, it is readily apparent that there exists a need for a simple method and apparatus for injecting two component polyurethane or the like. By two component is meant polyurethane of two different colors, or polyurethane compositions having different physical and/or chemical properties for each molding operation. Alternatively, two similar compositions can be used.
The object of the present invention is to provide a method and an apparatus for injecting two component polyurethane soles for footwear which are relatively simple and which facilitate the production of such soles.
According to one aspect of the invention, there is provided a method for molding two component soles for footwear of polyurethane or the like comprising the steps of molding a first sole portion at a first molding station; moving the first sole portion along a path of travel such that it returns to said first molding station after a predetermined period permitting at least partial curing of the first sole portion; and thereafter simultaneously molding a second sole portion on said first sole portion and a new, separate first sole portion at said first molding station.
According to another aspect of the invention, there is provided an apparatus for molding two component soles for footwear of polyurethane or the like comprising a turntable; a plurality of spaced apart mold bottoms carried by said turntable; mold top means carried by said turntable for forming a first mold cavity with each of said mold bottoms one at a time; mold sides; a plurality of lasts carried by said turntable for receiving uppers and forming second mold cavities with said mold bottoms and mold sides; said lasts being equal in number to said mold bottoms; and means for simultaneously injecting one component into a first mold cavity and the second component into a second mold cavity, whereby simultaneously to complete a two component sole and mold a new, separate first sole portion.
By simultaneously injecting one component of a two component sole into one mold and a second component of a two component sole into another mold at the same molding station, the number of molding stations can be substantially reduced. Moreover, after the initial injection of a first component into a plurality of molds on a turntable to form a plurality of first sole portions, simultaneous injection of the second component to complete the soles and injection of new first components can take place on a continuous basis. It is also possible to use a single source of polyurethane resin and a single injection unit. With such an arrangement, three material feed systems are required instead of four. One feed system supplies the polyurethane resin to a pair of mixing devices, the second system supplies the hardener and other materials, e.g. coloring agents to the first component mixing device and injection nozzle, and the third system supplies the hardener and other materials to the second component mixing device and injection nozzle. Thus, not only do the method and apparatus of the present invention facilitate production, but they can lead to a substantial saving in machinery costs. The use of a single injection unit having two nozzles means that the safety features normally required are also reduced in number, i.e. safety features may be required for one injection unit instead of two.
With the method and apparatus of the present invention, the molds pass an operator immediately before molding operations, and the face of the molds containing the injection ports can be cleaned. In known two component molding methods, molding of one component occurs at a first molding station and molding of a second component occurs at a second molding station remote from the first station. Thus, if the second injection port becomes blocked during the first molding step, it may be difficult or impossible to effect the second molding step unless an operator is present to clean the face of the mold containing the injection ports. In other words, instead of two cleaning operations for molding at two separate locations, only one cleaning operation is required with the method and apparatus of the present invention.